HIGH STRENGTH Be/Cu ALLOYS WITH IMPROVED ELECTRICAL CONDUCTIVITY

ABSTRACT

The electrical conductivity of a wrought processed, high strength, age hardened Be—Cu alloy is enhanced by overaging the alloy in manufacture.

SUMMARY

In accordance with this invention, the electrical conductivity of a wrought processed, high strength, age hardened Be—Cu alloy is significantly enhanced if the alloy is overaged when made.

Thus, this invention provides a new aged hardened wrought Be/Cu alloy consisting essentially of about 1.60-2.00 wt. % Be, at least about 0.15 wt. % Co+Ni but no more than about 0.6 wt. % Co+Ni+Fe, optionally up to about 0.5 wt. % in total of Si, Al, Zr and Ti, the balance being copper and incidental impurities, the alloy having been overaged in manufacture.

In addition, this invention also provides a process for increasing the electrical conductivity of a wrought, solution annealed, age hardenable Be/Cu alloy, the alloy consisting essentially of about 1.60-2.00 wt. % Be, at least about 0.15 wt. % Co+Ni but no more than about 0.6 wt. % Co+Ni+Fe, optionally up to about 0.5 wt. % in total of Si, Al, Zr and Ti, the balance being copper and incidental impurities, the process comprising overaging the alloy by an amount sufficient so that the electrical conductivity of the alloy produced is greater by at least 3% IACS than the electrical conductivity of an otherwise identical alloy peak aged during manufacture.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph schematically illustrating the relationship between underaging, peak aging and overaging in the manufacture of Be—Cu alloys.

DETAILED DESCRIPTION

In accordance with this invention, the electrical conductivity of a wrought, age hardened, high strength “gold” Be—Cu alloy is enhanced by overaging the alloy in manufacture.

High Strength, Wrought “Gold” Beryllium Copper Alloys

Beryllium copper alloys containing about 0.2 to 2.9 wt. % Be develop attractive combinations of strength, hardness and electrical conductivity when precipitation (age) hardened. See, Harkness et al., Beryllium-Copper and Other Beryllium-Containing Alloys, Metals Handbook, Vol. 2, 10th Edition, pages 403 to 427, © 1983, ASM International.

The excellent physical properties of these alloys arise through a precipitation-hardening mechanism in which fine copper beryllide precipitates form in the copper matrix. So long as beryllium is present in an appropriate amount, a small but suitable portion of this beryllium forms copper beryllide precipitates of small particle size during precipitation hardening. These small precipitate particles uniformly distribute in the copper matrix, thereby enhancing its strength.

The crystal structure and hence properties of many age hardenable alloys (including the Be—Cu alloys of interest here) can be significantly affected by subjecting the alloy to substantial, uniform mechanical working (deformation without cutting), typically on the order of 11%, 21%, 37% or more in terms of area reduction. Accordingly, most alloys of this type are available commercially either in wrought (worked) form or in cast (unwrought) form. See, for example, Kirk Othmer, Concise Encyclopedia of Chemical Technology, Copper Alloys, pp 318-322, 3d. Ed., © 1985. See, also, the APPLICATION DATA SHEET, Standard Designation for Wrought and Cast Copper and Copper Alloys, Revision 1999, published by the Copper Development Association.

The present invention is primarily applicable to wrought Be—Cu alloys—i.e., Be—Cu alloys which have been subjected in manufacture to mechanical deformation carried out to effect a noticeable change in the crystal structure and properties of the alloy obtained.

Commercially, wrought Be—Cu alloys are available in two forms, those exhibiting high strength and those exhibiting high electrical conductivity. High strength alloys typically contain about 1.6-2.0 wt. % Be, at least about 0.15 wt. % Co+Ni but no more than about 0.6 wt. % Co+Ni+Fe, optionally up to about 0.5 wt. % in total of Si, Al, Zr and Ti, with the balance being copper and incidental impurities. Desirably, the total concentration of Be+Co+Ni+Fe+Cu in the alloy is at least 99.5 wt. %. Preferably, the total concentration of these ingredients in the alloy is at least 99.7 wt. %, 99.8 wt. %, 99.9 wt. %, or even 99.95 wt. %. Because of their relatively high Be content, these high strength Be—Cu alloys exhibit a noticeable gold luster and hence are sometimes referred to as “gold” alloys. Specific examples of commercially available high strength wrought Be—Cu alloys include Alloy C17000, Alloy C17200 and Alloy C17300.

These high strength Be—Cu alloys exhibit 0.2% yield strengths of about 70 to 175 or even 180 ksi. Because there is a trade off between strength and electrical conductivity, these alloys exhibit relatively low electrical conductivities, typically about 17 to 28% IACS and always <30% IACS.

In contrast to these high strength alloys, the high conductivity wrought Be—Cu alloys typically contain about 0.15-0.60 wt. % Be, at least about 1.0 wt. % Co+Ni but no more than about 2.7 wt. % Co+Ni+Fe, optionally up to about 0.5 wt. % in total of Si, Al, Zr and Ti, with the balance being copper and incidental impurities. Because of their relatively low Be content, these high conductivity alloys exhibit a noticeable reddish or coral gold luster and hence are sometimes referred to as “red” Be—Cu alloys. Specific examples of commercially available high conductivity wrought Be—Cu alloys include Alloy C17410, Alloy C17460 and Alloy C17510. These alloys exhibit much higher electrical conductivities, typically about 45 to 60% IACS but much lower 0.2% yield strengths, typically about 95 to 125 ksi, relative to the high strength Be—Cu alloys.

This invention relates to the high strength (“gold”) wrought Be—Cu alloys described above, it having been found that the electrical conductivities of these alloys can be significantly improved, without encountering a corresponding substantial decrease in their 0.2% yield strengths, if they are overaged in manufacture. Alloys in which the concentration of each of Fe, Si and Al (and preferably also Ti and Zr) is no greater than 0.02 wt. %, preferably no greater than 0.01 wt. %, are especially interesting, as the electrical conductivities of these alloys can be increased even more.

Be—Cu Alloys—Precipitation Hardening

Forming useful products from wrought Be—Cu alloys derived from an ingot (“casting” or “as cast” alloy) typically involves a series of heating and working steps to impart the desired shape, grain structure and properties to the alloy. These steps in the aggregate can be considered as constituting

a shaping regimen for changing the bulk shape of the alloy as derived from the ingot into a shape approaching the final desired shape of the product (a “near net shape”) and also for imparting a finer, more nearly uniform grain structure to the alloy, and

a precipitation hardening regimen for nucleating and growing the fine copper beryllide precipitates responsible for hardening.

Commercially, the shaping regimen involves one or more working steps and solution heat treatment (annealing) steps. Annealing is typically done by heating the alloy at about 1375° F. to about 1900° F. (745° C. to 1040° C.) for <15 min to about 1 hr or even about 2 hr at temperature, the time increasing with increasing section thickness. The high strength (“gold”) alloys are annealed at the low end of this range, up to about 1500° F. (815° C.). The purpose is to put beryllium and other alloying additions into solid solution, followed by rapid quenching to retain these ingredients in solid solution. The optimum annealing time is typically determined from aging response studies, mechanical testing and microscopic examination of the alloy. Annealing dissolves a maximum amount of beryllium and other components that might be present, simultaneously producing a grain structure which is more nearly uniform. Internal stresses in the alloy are also reduced by annealing. Working can be done either at elevated temperatures (“hot working”) or at lower temperatures such as room temperature (“cold working”). Both working and annealing may be done multiple times, especially if change in shape is large, with a final solution anneal usually being done last.

Precipitation hardening (“age hardening”) of Cu—Be alloys is typically done by heating the alloy at about 500°-1300° F. (260°-705° C.) for a time sufficient to develop maximum hardness in the alloy, typically between about 15 minutes to 8 hours. The high strength (“gold”) alloys are age hardened in the lower region of this range, up to about 750° F. (400° C.) or even 800° F. (430° C.). In general, each Be—Cu alloy has its own particular time/temperature combination leading to maximum hardness, meaning that if the alloy is heated either too little or too much its hardness and other properties are less than optimal. Thus, it is conventional to refer to such alloys as being “peak aged” if age hardened at or near optimal time/temperature conditions, or as underaged or overaged if heated too little or too much.

This is illustrated in FIG. 1, which is a graph schematically illustrating the relationship between the hardness of a typical Be—Cu alloy and aging time at a constant age hardening temperature. As shown in this FIGURE, when the alloy is heated to age hardening temperature after final solution annealing, the hardness of the alloy increases from an initial value to a peak or maximum value over time. Then, as the alloy continues to be heated, the hardness of the alloy decreases from its maximum down to a significantly lower level. The alloy is said to be “peak aged” if age hardened at or near optimal time/temperature conditions, or as “underaged” or “overaged” if heated too little or too much, as illustrated in the FIGURE.

In accordance with the present invention, it has been found that the electrical conductivities of high strength, wrought Be—Cu alloys can be significantly improved, without encountering a corresponding substantial decrease in their 0.2% yield strengths, if they are overaged in manufacture.

The Overaging Step

As indicated above, the specific conditions of time and temperature which will result in peak aging a particular high strength, wrought Be—Cu alloy vary from alloy to alloy and can be easily determined by routine experimentation. In accordance with this invention, the specific conditions of time and temperature selected for carrying out age hardening are selected so that alloy obtained is overaged. Desirably, the alloy is overaged so that the electrical conductivity of the alloy obtained is greater by at least 3% IACS than the electrical conductivity of an otherwise identical alloy which has been peak aged in manufacture. Preferably, the alloy is overaged so that its electrical conductivity is greater than the electrical conductivity of the peak aged alloy by at least 5% IACS, 7.5% IACS or even 10% IACS. Normally, this means that the alloy produced will have an electrical conductivity of at least 28% IACS, at least 30% IACS, at least 33% IACS or even 35% IACS or more.

Overaging the high strength, wrought Be—Cu alloys of this invention can normally be done by heating at temperatures ranging from about 650° F. (343° C.) to 775° F. (413° C.) or more for periods of time as short as 30 seconds to as long as 7 hours or more or even 15 hours or more. In this regard, it will be appreciated that the time/temperature regimen necessary to achieve a particular level of age hardening depends not only on the chemical composition of the alloy but also on its size as well as the method by which it is heated. Thus, higher temperatures and/or longer treatment times are normally necessary where the alloy is in the form of a large bulky mass and/or the age hardening step is done by batch operation in a furnace. In contrast, shorter treatment times can normally be used where smaller, less bulky objects are being age hardened and/or if age hardening is done by a continuous operation, such as for example when a continuous strip is moved through a stationary furnace. In accordance with this invention, workpieces made from high strength, wrought Be—Cu alloys, regardless of their shape or size, are overaged so as to provide enhanced electrical conductivity. Skilled metallurgists can easily determine the particular conditions of time and temperature at which this should be done for particular alloy products by routine experimentation.

Also, as well known in the art, age hardening can be done in a single step or in multiple steps, if desired. In addition, if multiple steps are used, the workpiece can also be allowed to cool below the age hardening temperature (i.e., below a temperature at which the alloy will age harden as a practical matter), or even to ambient, between these steps, if desired. Moreover, if age hardening is done in multiple steps, it is customary practice although not required that the most severe conditions of time and temperature are encountered in the final age hardening step. All of these variants are applicable to the present invention.

Heat-Treatable Vs. Mill Hardened Alloys

Age hardenable alloys in general, and the high strength, wrought Be—Cu alloys of this invention in particular, are commercially available from the mill which produces these alloys in heat-treatable form as well as in mill hardened form. In this context, a “mill-hardened” alloy is an alloy which has already been fully wrought processed and age hardened by the mill where the alloy is made from a melt, whereas a “heat-treatable” alloy has not. Products made from mill hardened alloys are typically sold to customers who intend to do only final minor shaping or forming of the products, without final heat treatment. Stamped current-carrying springs or terminals generally involving no severe bends are a good example of such a product. In contrast, heat treatable alloys are typically sold to customers who plan to do significant additional mechanical deformation during stamping such as, for example, severe bending, coining, etc., since this allows a softer alloy to be mechanically deformed before the final age hardening step. Normally, customers who buy heat treatable alloys carry out the final age hardening step themselves.

This invention is applicable to both heat treatable and mill hardened alloys. That is to say, the advantages of this invention, increasing the electrical conductivity of a high strength, wrought Be—Cu alloy, can be achieved whether overaging is done by the mill where the alloy is made from a melt or by a direct or indirect customer of the mill who accomplishes the final age hardening treatment itself.

Alloy Strip

Most commonly, this invention will be used in connection with making alloy strip. In this context, “strip” means an alloy product having a regular cross-section and an indeterminate length many times larger than its cross-section. Most strip products are produced by semi-continuous casting or continuous casting. In the case of semi-continuous casting a thick section cast billet is typically converted to thin section wire or strip by hot extrusion or hot rolling, respectively. Some of these products like wires and thin strip, for example, are thin enough so that they are readily flexible and hence can formed into coils by being wound up on reels or the like for storage and/or shipment in bulk. Such coils usually contain multiple courses or revolutions of the strip, from as few as 5 or 10 to as many as 100, 250, 500 or even a 1,000 or more, depending on thickness, whereby the multiple revolutions are closely packed upon one another. In other cases, such as thicker section “plate” or “bar”, where the product is too inflexible to be wound up on a reel, the product is cut into sections of a predetermined convenient length such as 10, 20, 30 or 40 feet, for example, with multiple sections being closely-packed such as by being bundled together in a side-by-side arrangement for storage and/or shipment in bulk. “Strip” products are understood to be thinner than “plate” or “bar” products, which are thick enough to be essentially rigid. In addition, “strip” coils of wide producing mill width may be slit into multiple narrow coils, each wound on a separate reel. The narrow slit coils may be handled singly or in stacks of multiple slit cut coils for storage and shipment.

This invention is broadly applicable to all strip product, whether present as a single, continuous piece of indeterminate length or in multiple sections. In addition, this invention is applicable to thin strip and/or strip sections being age hardened in a batch operation such as, for example, when multiple strip sections, are arranged in bulk (i.e., closely packed upon one another) and heated in an age hardening furnace for hours. Similarly, this invention is also applicable to thin strip being age hardened in a continuous operation such as, for example, when a continuous strip of indeterminate length is continuously passed through a stationary furnace for relatively short residence times, for example, on the order of 0.5 to 20 minutes.

So, for example, in one approach for age hardening contemplated by this invention, a continuous alloy strip of indeterminate length in the form of a coil wound up on a reel is overaged in bulk by heating the entire coil in a furnace (“batch age hardening”). In another approach, a continuous alloy strip of indeterminate length (i.e., unwound) is continuously fed through a stationary age hardening furnace (“continuous age hardening”). In still another approach, a continuous alloy strip is stamped into individual parts and the individual parts are age hardened in a batch operation in bulk (i.e., closely-packed) by being carried on carrier strips, the carrier strips being arranged in a coil on a reel, or the stamped parts can be arranged as loose parts closely packed in trays, baskets or the like. In yet another approach, individual stamped parts are age hardened separately (i.e., not closely-packed) such as, for example, by being carried in small lots in trays or baskets in a link-belt atmosphere furnace or by immersion in a high heat transfer coefficient medium such as molten salt.

Thus, this invention contemplates a number of specific embodiments for producing age hardened wrought Be—Cu alloy strip with improved electrical conductivities, as more fully discussed below:

Mill-Hardened Alloys

In each of these embodiments, an alloy containing about (1.60-2.00)Be-(0.15 min Co+Ni; 0.6 max Co+Ni+Fe)—Cu in which copper+named additions is 99.5 wt % minimum is melted, cast, hot rolled, optionally solution annealed, with any surface oxides optionally removed by pickling or surface milling, cold rolled, solution annealed and optionally pickled one or more times to a “ready-to-finish” thickness, at which time the strip is given a final solution anneal at about 1390° F. to about 1450° F. or even 1500° F. and pickled, followed by optional cold rolling.

Embodiment 1

After cold rolling in an amount of 0% to about 50% to final thickness, a continuous alloy strip of indeterminate length in the form of a coil wound up on a reel is overaged in bulk by heating the entire coil in a furnace (“batch age hardening”) at about 650° F. to 730° F. for 0.5 hour to 7 hours (e.g., about 650 F for about 7 hours, or about 730° F. for about 0.5 hour) to achieve discrete targeted 0.2% offset yield strengths ranging from about 70 ksi to about 165 ksi or higher, followed by final pickling.

The entire length of strip, overaged in this manner, will typically exhibit an electrical conductivity of about 30% IACS to about 35% IACS. Because of the trade-off between electrical conductivity and yield strength, alloys subjected to more extensive overaging will develop lower yield strengths than less extensively overaged alloys of the same chemical composition. Nonetheless, the yield strengths of these alloys are still acceptable for most “high strength” applications and generally at least as great or somewhat greater than the strengths of traditional non-overaged mill hardened high strength Be—Cu alloys having conductivity less than 30% IACS.

Embodiment 2

After cold rolling in an amount of 11% to about 16% to final thickness, a continuous alloy strip of indeterminate length (i.e., unwound) is continuously fed through a stationary age hardening furnace (“continuous age hardening”) where it is subjected to a first overaging heat treatment by heating at about 730° F. to about 775° F. for a residence time of about 30 sec to 240 sec (e.g., about 730°-750° F. for about 160-240 seconds, or to about 775° F. for about 30-35 sec). The strip is then wound up on a reel and the coil so formed subjected to second overaging heat treatment step in bulk by heating the entire coil in a furnace (“batch age hardening”) at about 615° F. to about 800° F. for about 1 hour to 5 hours (e.g., about 615°-707° F. for about 5 hours, or about 775°-800° F. for about 1 hour) followed by final pickling.

The product obtained will typically exhibit an electrical conductivity of about 30% IACS or more and more typically 35% IACS or more, or even 36% IACS or more. In addition, these alloys will also have 0.2% offset yield strengths after the second aging step ranging from about 80 ksi or 87 ksi with 90 deg bend formability of about 0 R/t Longitudinal and 0 R/t Transverse, to about 120 ksi or 136 ksi with 90 deg bend formability of about 0.2 R/t or 1.0 R/t Longitudinal and about 0.4 R/t or 2.7 R/t Transverse, to about 145 ksi or 153 ksi with 90 deg bend formability of about 0.8 R/t or 1.8 R/t Longitudinal and about 0.8 R/t or 3.3 R/t Transverse.

In each case above, bend formability is expressed as the smallest permissible ratio of 90 degree bend radius R divided by the strip thickness t for no cracking. The smaller the value of R/t, the better the formability. Longitudinal bends have the bend axis perpendicular to the rolling direction. Transverse bends have the bend axis parallel to the rolling direction. Generally, formability is better (smaller R/t) for lower yield strengths and worse (larger R/t) for higher strengths.

Embodiment 3

Embodiment 3 is the same as Embodiment 2, except that cold rolling is done in an amount of about 8% to about 21% and, in addition, the arrangement of the continuous vs. batch age hardening steps is reversed. That is to say, in this embodiment, the first age hardening step is conducted in bulk with the alloy strip being in a coil wound up on a reel, while the second age hardening step is conducted with the unwound alloy strip being continuously fed through a stationary furnace. In this approach, the first age hardening step is conducted at about 650° F. to 750° F. for about 1.5 hr to 3 hr (e.g., about 650°-725° F. for 3 hours or 750° F. for about 1.5 hr) while the second age hardening step is done at about 730° F. to about 750° F. for a residence time of about 3 min to about 15 min (e.g., about 730 F for about 15 min or about 750° F. for about 3 min) followed by final pickling and optional mechanical brushing.

This will typically achieve electrical conductivities of about 29-30% IACS, at discrete targeted 0.2% offset yield strengths ranging from about 110 ksi or 125 ksi to about 140 ksi or 148 ksi or even 155 ksi with 90 deg bend formabilities of at least about 1.6 to 2.0 R/t Longitudinal and about 2.0 to 3.2 R/t Transverse.

Embodiment 4

Embodiment 4 is the same as Embodiments 2 and 3, except that cold rolling is done in an amount of about 0% to about 21% and, in addition, both age hardening steps are conducted in bulk with the alloy strip being in a coil wound up on a reel. In this embodiment, the first age hardening step is conducted at about 650° F. to 750° F. for about 2 hr to 3 hr, while the second age hardening step is done at about 700° F. to about 750° F. for about 3 hours to about 5 hours (e.g., about 700° F. for about 5 hours followed by final pickling and optional mechanical brushing.

This will typically achieve electrical conductivities of at least about 32% IACS and more typically at least about 34% IACS or even as high as 39% IACS, and discrete targeted 0.2% offset yield strengths ranging from about 95 ksi to about 110 ksi.

Embodiment 5 Hypothetical

Embodiment 5 is the same as Embodiments 2-4, except that cold rolling is done in an amount of about 11% to about 37% and, in addition, both age hardening steps are conducted in a continuous mode, i.e., with a continuous alloy strip of indeterminate length being continuously fed through a stationary age hardening furnace. In this approach, the first age hardening step is conducted at about 730° F. to about 775° F. for about 30 sec to 240 sec (e.g., about 730°-750° F. for about 160-240 seconds, or to about 775° F. for about 30-35 sec) while the second age hardening step is done at about 730° F. to about 750° F. for about 3 min to about 15 min (e.g., about 730° F. for about 15 min or about 750° F. for about 3 min) followed by final pickling and optional mechanical brushing.

This is estimated to achieve electrical conductivities of at least about 30% IACS and more typically at least about 32% IACS or even 35% IACS, and discrete targeted 0.2% offset yield strengths ranging from about 125 ksi to about 135 ksi.

Embodiment 6 Hypothetical

Embodiment 6 is the same as Embodiment 1, except that in Embodiment 6, age hardening is accomplished in a single age hardening step conducted in the continuous mode, i.e., with a continuous alloy strip of indeterminate length being continuously fed through a stationary age hardening furnace. In this approach, this age hardening step is conducted at about 730° F. to about 775° F. for a residence time of about 4 min to about 20 min (e.g., about 730° F. for about 20 min or about 775° F. for about 4 min to about 15 min followed by final pickling and optional mechanical brushing.

This is estimated to achieve electrical conductivities of at least about 30% IACS and more typically at least about 32% IACS or even 35% IACS, and discrete targeted 0.2% offset yield strengths ranging from about 95 ksi to about 135 ksi.

Heat Treatable Alloys Embodiments 7-12

These embodiments are the same as Embodiments 1-6 above except that, prior to age hardening, the continuous alloy strip coil is slit into narrow sections and the individual strip sections are subjected to various additional mechanical shaping operations such as stamping, bending, forming, etc.

Embodiment 7

Thus, Embodiment 7 is the same as Embodiment 1, except that in Embodiment 7 the strip sections, stamped or formed into parts, are arranged in bulk (i.e., closely-packed) by being carried on carrier strips, the carrier strips being arranged in a coil on a reel. Alternately, the strip sections can be arranged as loose parts closely packed in trays, baskets, or the like.

Embodiment 8

Embodiment 8 is the same as Embodiment 2, except that in Embodiment 8 the strip sections are arranged separately (i.e., unwound and not closely packed) in the first age hardening step, such as stamped or formed parts on carrier strips or loose parts carried in small lots in trays or baskets in a link-belt atmosphere furnace or by immersion in a high heat transfer coefficient medium such as molten salt. Then these strip sections are arranged in bulk (i.e., closely-packed) by being carried on carrier strips, which in turn are arranged in a coil on a reel. Alternately, these strip sections can be arranged as loose parts closely packed in trays or the like in the second age hardening step.

Embodiment 9

Embodiment 9 is the same as Embodiment 3, except that in the first age hardening step multiple strip sections are arranged in bulk (i.e., closely-packed) by being carried on carrier strips, the carrier strips being arranged in a coil on a reel. Alternately, these strip sections can be arranged as loose parts closely packed in trays or the like. Then in the second age hardening step, these strip sections are arranged individually or separately (i.e., not closely packed) such as by being carried spaced apart in small lots in trays or baskets in a link-belt atmosphere furnace or by immersion in a high heat transfer coefficient medium such as molten salt.

Embodiment 10

Embodiment 10 is the same as Embodiment 4, except that in both the first and second age hardening steps the alloys sections are arranged in bulk (i.e., closely-packed) by being carried on carrier strips, the carrier strips being arranged in a coil on a reel, or by being arranged as loose parts closely packed in trays or the like.

Embodiments 11 and 12 Hypothetical

Embodiments 11 and 12 are the same as Embodiments 4 and 5, respectively, except that prior to the second age hardening step, the individual alloy sections in Embodiments 11 and 12 are subjected to various additional mechanical shaping operations, as indicated above.

In a variation of all of the above embodiments, the incidental impurity content of the melt is restricted to about 0.01-0.02 wt % maximum each of Fe, Si, Al, Zr and Ti. This increases the resulting electrical conductivity after averaging by about a net of about 3% IACS to about 6% IACS compared to an alloy with commercial levels of the named impurity elements.

WORKING EXAMPLES

In order to more thoroughly illustrate this invention, the following working examples are provided. In these examples, high strength (“gold”) wrought Be—Cu alloy strip products were prepared by forming a melt of the indicated composition, and then producing a wrought processed aged hardened strip product by casting the melt into a billet, hot rolling the billet into a strip, cold rolling the strip to a selected ready-to-finish thickness, final solution annealing the cold rolled strip, optionally cold working the annealed strip by an amount of 0-21%, or even 37% or 50%, in terms of area reduction, and then overaging the cold worked strip in one or two age hardening steps.

The following alloy compositions were tested:

TABLE I Alloy Compositions Alloy Be (wt %) Co (wt %) Impurities (wt %) Cu A 1.80-2.00 0.2 Co min- Standard Purity Balance 0.6(Co + Ni + Fe) max Fe, Si, Al EACH ≧ 0.02-0.03 B 1.80-2.00 0.2 Co min- High Purity Balance 0.6 Co + Ni + Fe) max Fe, Si, Al EACH ≦ 0.02 C 1.60-1.79 0.2 Co min- Standard Purity Balance 0.6(Co + Ni + Fe) max Fe, Si, Al EACH ≧ 0.02-0.03 D Nominal 1.9 Nominal 0.15 Standard Purity Balance Fe, Si, Al EACH ≧ 0.02-0.03 E Nominal 1.85 Nominal 0.15 Medium Purity Balance Fe, Si, Al EACH = 0.01-0.03 F Nominal 1.9 Nominal 0.15 High Purity Balance Fe, Si, Al EACH ≦ 0.02

The strip products obtained were then tested for 0.2% Yield Strength by ASTM E8 and/or Rockwell Hardness by ASTM E18, and Electrical Conductivity by ASTM B193. A few of the strip products were also tested for bend formability by ASTM E290.

Two different sets of experiments were conducted, these two sets corresponding to Embodiments 1 and 4 of this invention, as described above.

Set 1 Comparative Examples A-K and Examples 1-21

In this set of examples, a continuous alloy strip of indeterminate length was processed in general accordance with the procedure of Embodiment 1 above. In particular, the alloy strip was age hardened in bulk in a single age hardening step by arranging the strip in the form of a coil having multiple courses or revolutions closely packed on one another and heating the entire coil in a furnace. Alternatively, small individual panels of strip were laboratory-age hardened in a small furnace to simulate bulk coil age hardening per Embodiment 1. Comparative Examples A-C, which illustrate the results obtained when these alloys are peak aged in accordance with the prior art approach of peak aging rather than the overaging approach of this invention, are provided for comparative purposes. Comparative Examples A-C represent summaries of earlier experiments in which bulk heat treatment was simulated in the laboratory. Comparative Examples D-K represent current experiments showing conductivity less than 30% IACS being achieved by peak age hardening, Comparative Example F relates approximately to a relative maximum strength in the aging response curve for Alloy A when age hardened at 730 F, shorter or longer times than about 0.5 hr resulting in less than maximum strength at this aging temperature.

The following results were obtained:

TABLE II Set 1 Results Elect. Cold 0.2% YS or Cond. Form Ex Alloy Ann. Work Age 1 Age 2 Hard % IACS [L/T] A A 1425 F. 0-37% 600 F./3-2 hr None 140-205 22-28 NA** typical ksi HRC36-45 B C 1425 F. 0-37% 600 F./3-2 hr None HRC40-42 22.1-23.6 NA typical C E or F 1450 F. 0-37% 650 F./3 hr None HRC42-43 30.4-30.1 NA D A 1400 F. 0% 600 F./3 hr None HRC40 24.1 ND* E A 1450 F. 0% 600 F./3 hr None HRC40 23.8 ND F A 1390 or 21% 730 F./0.5 hr None 142 ksi 24.7 ND 1420 F. G D 1400 F. 0% 600 F./3 hr None HRC40 23.9 ND H D 1450 F. 0% 600 F./3 hr None HRC40 23.8 ND I B 1400 F. 0% 600 F./3 hr None HRC37 28.4 ND J B 1450 F. 0% 600 F./3 hr None HRC38 28.0 ND K F 1450 F. 0% 600 F./3 hr None HRC39 27.3 ND 1 A 1400 F. 0% 650 F./3 hr None HRC41 28.4 ND 2 A 1450 F. 0% 650 F./3 hr None 160 ksi 29.4 ND HRC42 27.9 3 A 1420 F. 16% 650 F./1.5 hr None 163 ksi 28.1 3/3.8 R/t 4 A 1420 F. 16% 650 F./3 hr None 162 ksi 29.3 3/3.9 R/t 5 A 1450 F. 21% 650 F./3 hr None 163 ksi 30.4 ND 6 A 1390 or 0% 730 F./3.5 hr None  75 ksi 34.7 0/0 R/t 1420 F. 7 A 1390 or 0% 730 F./6.5 hr None  82 ksi 34.8 0/0 R/t 1420 F. 8 A 1390 or 11% 730 F./0.5 hr None 134 ksi 30.1 ND 1420 F. 9 A 1390 or 11% 730 F./5.5 hr None 111 ksi 34.1 ND 1420 F. 10 A 1390 or 16% 730 F./0.5 hr None 143 ksi 29.4 ND 1420 F. 11 A 1390 or 16% 730 F./5.5 hr None 121 ksi 34.8 ND 1420 F. 12 A 1390 or 21% 730 F./5.5 hr None 111 ksi 34.6 ND 1420 F. 13 A 1390 or 50% 730 F./3 hr None 114 ksi 32.6 ND 1420 F. 14 B 1400 F. 0% 650 F./3 hr None HRC35 34.8 ND 15 B 1450 F. 0% 650 F./3 hr None 161 ksi 32.0 ND HRC39 33.6 16 B 1450 F. 21% 650 F./3 hr None 161 ksi 32.7 ND 17 D 1400 F. 0% 650 F./3 hr None HRC42 27.7 ND 18 D 1450 F. 0% 650 F./3 hr None HRC42 27.5 ND 19 E 1450 F. 0% 650 F./3 hr None HRC38 30.5 ND 20 F 1450 F. 0% 650 F./3 hr None 144 ksi 33.8 ND HRC40 32.4 21 F 1450 F. 21% 650 F./3 hr None 150 ksi 33.7 ND *ND = No data **NA = not applicable

As can be seen from Table II, the electrical conductivities of many of the alloys obtained in accordance with this embodiment of the invention were above 30% IACS, while the electrical conductivities of the remaining alloys were at least about 28% IACS, which is essentially the maximum electrical conductivity obtainable by the prior art approach of peak aging. The contribution of high impurity content to reduced electrical conductivity for a given thermal treatment is demonstrated by Examples 10, 19 and 20.

Set 2 Examples 22-53

In this set of examples, an alloy strip of indeterminate length was age hardened in general accordance with the procedure of Embodiments 2, 3 and 4 above. In particular, the alloy strip was subjected to two age hardening steps, both of which were carried out with the alloy strip being arranged in bulk in the form of a coil and heating the entire coil in a furnace.

The following results were obtained:

TABLE III Set 2 Results Elect. Cold 0.2% YS/ Cond. Ex Alloy Ann. Work Age 1 Age 2 Hard % IACS Form [L/T] 22 A 1390 or 11% 730 F./2′36″ 615 F./3 hr 153 ksi 29.4 1.8/1.8 R/t 1420 F. 23 A 1390 or 11% 730 F./2′36″ 615 F./5 hr 151 ksi 30.2 1.8/1.8 R/t 1420 F. 24 A 1390 or 11% 730 F./2′36″ 707 F./1 hr 126 ksi 32.5 0.5/1.0 R/t 1420 F. 25 A 1390 or 11% 730 F./2′36″ 707 F./5 hr 111 ksi 35.6 0.3/0.3 R/t 1420 F. 26 A 1390 or 11% 730 F./2′36″ 800 F./3 hr  87 ksi 33.7   0/0 1420 F. 27 A 1390 or 11% 730 F./2′36″ 800 F./5 hr  82 ksi 34.7   0/0 1420 F. 28 A 1390 or 16% 730 F./2′25″ 707 F. 1 hr 146 ksi 29.6 0.8/0.8 R/t 1420 F. 29 A 1390 or 16% 730 F./2′25″ 707 F./3 hr 131 ksi 32.2 1.0/1.0 R/t 1420 F. 30 A 1390 or 16% 730 F./1′33″ 707 F. 1 hr 148 ksi 29.9 1.2/2.2 R/t 1420 F. 31 A 1390 or 16% 730 F./1′33″ 707 F./3 hr 131 ksi 32.5 0.8/1/0 R/t 1420 F. 32 A 1390 or 16% 730 F./35″ 707 F. 1 hr 144 ksi 30.4 1.0/3.3 R/t 1420 F. 33 A 1390 or 16% 730 F./1′33″ 707 F./3 hr 132 ksi 32.1 0.6/0.8 R/t 1420 F. 34 A 1390 or 16% 775 F./2′10″ 707 F. 1 hr 136 ksi 30.5 0.2/1.0 R/t 1420 F. 35 A 1390 or 16% 730 F./1′33″ 707 F./3 hr 126 ksi 32.5 0.4/0.6 R/t 1420 F. 36 A 1390 or 16% 775 F./4′0″ 707 F. 1 hr 136 ksi 31.2 0.8/0.8 R/t 1420 F. 37 A 1390 or 16% 775 F./4′0″ 707 F./3 hr 123 ksi 32.9 0.4/0.4 R/t 1420 F. 38 C 1390 or 16% 730 F./2′36″ 707 F. 1 hr 135 ksi 29.6 0.9/2.7 R/t 1420 F. 39 C 1390 or 16% 730 F./2′36″ 707 F./3 hr 126 ksi 32.2 0.8/1.4 R/t 1420 F. 40 A 1420 F. 16% 650 F./1.5 hr 730 F./3.5′ 153 ksi 27.9   2/3.2 R/t 41 A 1420 F. 16% 650 F./1.5 hr 730 F./7′ 148 ksi 28.2 1.6/2.6 R/t 42 A 1420 F. 16% 650 F./1.5 hr 730 F./14′ 144 ksi 29.2 1.8/2.6 R/t 43 A 1420 F. 16% 650 F./3 hr 730 F./3.5′ 154 ksi 28.9 2.2/3.2 R/t 44 A 1420 F. 16% 650 F./3 hr 730 F./7′ 148 ksi 28.9   2/2.8 R/t 45 A 1420 F. 16% 650 F./3 hr 730 F./14′ 144 ksi 29.5   2/2.4 R/t 46 A 1450 F. 0% 650 F./3 hr 750 F./5 hr 109 ksi 33.7 ND HRC33 32.5 47 A 1450 F. 21% 650 F./3 hr 750 F./5 hr 109 ksi 34.0 ND 48 B 1450 F. 0% 650 F./3 hr 750 F./5 hr 110 ksi 36.8 ND HRC30 38.5 49 B 1450 F. 21% 650 F./3 hr 750 F./5 hr 109 ksi 36.9 ND 50 D 1450 F. 0% 650 F./3 hr 750 F./5 hr HRC32 33.0 ND 51 E 1450 F. 0% 650 F./3 hr 750 F./5 hr HRC28 35.6 ND 52 F 1450 F. 0% 650 F./3 hr 750 F./5 hr  96 ksi 37.7 ND HRC31 38.5 53 F 1450 F. 21% 650 F./3 hr 750 F./5 hr 105 ksi 37.0 ND *ND = No data **NA = not applicable

As can be seen from these results, the electrical conductivities of most of the alloys obtained in accordance with these embodiments of the invention were above 30% IACS, while the electrical conductivities of the remaining alloys were at least about 29% IACS, which is essentially above the maximum electrical conductivity obtainable by the prior art approach of peak aging.

Although this invention has been thoroughly described above, many modifications can be made. All such modifications are intended to be included within the scope of the present invention, which is to be limited only by the following claims: 

1. An aged hardened wrought Be/Cu alloy consisting essentially of about 1.60-2.00 wt. % Be, at least about 0.15 wt. % Co+Ni but no more than about 0.6 wt. % Co+Ni+Fe, optionally up to about 0.5 wt. % in total of Si, Al, Zr and Ti, the balance being copper and incidental impurities, the alloy having been overaged in manufacture.
 2. The alloy of claim 1, wherein the alloy is overaged by an amount sufficient so that the electrical conductivity of the alloy is greater by at least 3% IACS than the electrical conductivity of an otherwise identical alloy that has been peak aged in manufacture.
 3. The alloy of claim 2, wherein the amount of Be+Co+Ni+Fe+Cu in the alloy is at least 99.5 wt. %.
 4. The alloy of claim 3, wherein the alloy is overaged by an amount sufficient so that the electrical conductivity of the alloy is greater by at least 5% IACS than the electrical conductivity of the otherwise identical alloy
 5. The alloy of claim 1, wherein the alloy is overaged by an amount sufficient so that the electrical conductivity of the alloy is at least 28% IACS.
 6. The alloy of claim 5, wherein the alloy is overaged by an amount sufficient so that the electrical conductivity of the alloy is at least 30% IACS.
 7. The alloy of claim 6, wherein the alloy is overaged by an amount sufficient so that the electrical conductivity of the alloy is at least 33% IACS.
 8. The alloy of claim 7, wherein the alloy is overaged by an amount sufficient so that the electrical conductivity of the alloy is at least 35% IACS.
 9. The alloy of claim 1, wherein the alloy is in the form of a strip or stamped part.
 10. The alloy of claim 9, wherein the alloy is arranged in a closely-packed, bulk arrangement comprising either multiple revolutions of a continuous strip in a coil or multiple strip sections or stamped parts packed together in a side by side arrangement.
 11. The alloy of claim 1, wherein the alloy is made by the process comprising: (a) melting a composition containing the ingredients forming the alloy, (b) casting the melt into a billet, (c) hot rolling the billet into a strip, (d) cold rolling the strip to a selected ready-to-finish thickness, (e) final solution annealing the cold rolled strip at a temperature generally within a range of 1390° F. and 1500° F. followed by rapid quenching, (f) optionally cold working the annealed strip, and (g) overaging the cold worked strip to achieve an electrical conductivity of 30% IACS or more in the alloy product obtained.
 12. A process for increasing the electrical conductivity of a wrought, solution annealed, age hardenable Be/Cu alloy, the alloy consisting essentially of about 1.60-2.00 wt. % Be, at least about 0.15 wt. % Co+Ni but no more than about 0.6 wt. % Co+Ni+Fe, optionally up to about 0.5 wt. % in total of Si, Al, Zr and Ti, the balance being copper and incidental impurities, the process comprising overaging the alloy by an amount sufficient so that the electrical conductivity of the alloy produced is greater by at least 3% IACS than the electrical conductivity of an otherwise identical alloy peak aged during manufacture.
 13. The process of claim 12, wherein the amount of Be+Co+Ni+Fe+Cu in the alloy is at least 99.5 wt. %.
 14. The process of claim 13, wherein the alloy is overaged by an amount sufficient so that the electrical conductivity of the alloy is greater by at least 5% IACS than the electrical conductivity of the otherwise identical alloy
 15. The process of claim 13, wherein the alloy is overaged by an amount sufficient so that the electrical conductivity of the alloy is at least 28% IACS.
 16. The process of claim 15, wherein the alloy is overaged by an amount sufficient so that the electrical conductivity of the alloy is at least 30% IACS.
 17. The process of claim 16, wherein the alloy is overaged by an amount sufficient so that the electrical conductivity of the alloy is at least 33% IACS.
 18. The process of claim 17, wherein the alloy is overaged by an amount sufficient so that the electrical conductivity of the alloy is at least 35% IACS.
 19. The process of claim 12, wherein the alloy is in the form of a strip.
 20. The alloy of claim 19, wherein the strip is age hardened in a single age hardening step.
 21. The process of claim 19, wherein the strip is age hardened in multiple age hardening steps.
 22. The process of claim 21, wherein in at least one age hardening step, the alloy strip is arranged closely packed in bulk, wherein the alloy comprises either multiple strip sections or stamped parts arranged in a side by side relationship or multiple revolutions of a continuous alloy strip arranged in a coil, and in at least one other age hardening step, multiple alloy sections of alloy strip or stamped parts are arranged in a non-closely packed arrangement. 